Thermoelectric devices are well known. These devices utilize physics principals known as the Seebeck effect discovered in 1821 and the Peltier effect discovered in 1834. The Seebeck principle tells us that if two wires of different materials (such as copper and iron) are joined at their ends, forming two junctions, and one junction is held at a higher temperature than the other junction, a voltage difference will arise between the two junctions. The Peltier effect describes an inverse effect. If current is sent through a circuit made of dissimilar materials, heat will be absorbed at one junction and given up or evolved at the other junction.
Most thermoelectric devices currently in use today to generate electricity or for cooling utilize semiconductor materials (such as bismuth telluride) which are good conductors of electricity but poor conductors of heat. These semiconductors are typically heavily doped to create an excess of electrons (n-type) or a deficiency of electrons (p-type). An n-type semiconductor will develop a negative charge on the cold side and a p-type semiconductor will develop a positive charge on the cold side.
Since each element of a semiconductor thermoelectric device will produce only a few millivolts it is generally useful to arrange the elements in series so as to produce higher voltages for the generation of electricity or to permit use of higher voltages for cooling. Several techniques have been developed for arranging the semiconductor elements in series in thermoelectric devices. One such prior art method is shown in FIG. 20. In this device p and n type semiconductors are arranged in a checkerboard pattern and electrical jumpers are soldered, each to two different semiconductors, at the cold side and at the hot side so as to place all of the semiconductor elements in series with each other. This method is a low cost method and well established but has some limitations. Above 100.degree. C. the solders will defuse into the thermoelectric elements destroying them. In a high humidity atmosphere moisture may condense in the spaces between the elements and thermally short the module. The structure is not mechanically strong and easily fractures.
Another currently used method is the so-called eggcrate design shown in FIG. 21. Here an "eggcrate" made of insulator material separates the thermoelectric elements and permits electrical jumpers to be pressed against the elements to provide a good electrical connection without solder. It is also known to spray a conductor material on each side of these eggcrates to provide electrical connections. In prior art designs, the eggcrates are fabricated from individual strips which have been cut to shape having a series of slots using a precision laser cutter. The strips are then assembled into an eggcrate by interlocking the laser machined slots. All of the elements can be connected in series by proper construction of the eggcrate. Obviously it is possible in both devices to arrange for any desired number of elements to be in series. Thus, several elements in series may form a series set and this set could be arranged in parallel with other similar sets. The major disadvantage of prior art eggcrates is illustrated in FIG. 21. As is apparent in FIG. 21, gaps at junctions formed by the intersecting strips can permit electrical shorts between adjacent cells to occur, especially if electrical jumpers are applied using techniques such as metal spraying. Such shorts obviously could substantially degrade performance, reducing the power output of the module.
Also, prior art eggcrate modules are expensive due primarily to the fact that labor costs to assemble the eggcrates and to install the elements in the crates is expensive. What is needed is a gapless, lower cost thermoelectric eggcrate module.